Re: mehndi on mehndi?
No, the bride is not supposed to have mehndi on the mehndi day. The mehndi is done so that that seven suhaagans (married women) can apply them on the girl's hands for good luck. Nowadays a pan leaf (pam ka pata) is kept on the girl's hand's as the tradition of applying mehndi like jam has modernized into making intricate bridal designs on the girl's hands by a skilled mehndi artist.
A party is usually held at the bride's house with immediate family and friends a day before the baraat/nikkah/rukhsati and an artist comes over and applies the bridal mehndi on hands, arms and feet. The guests also get to apply mehndi as well on the same day.